Shunt reactors



Dec. 21, 1965 A. B. TRENCH 3,225,319

SHUNT REACTORS Filed Jan. 25, 1963 2 Sheets-Sheet 1 M/veA/Tw? ANT/w/v/ BFJRcA/I/ Wave/1 2W jkww Dec. 21, 1965 A. B. TRENCH 3,225,319

SHUNT REACTORS Filed Jan. 25, 1963 2 Sheets-Sheet 2 WWW/PW United States Patent 3,225,319 SHUNT REACTORS Anthony Barclay Trench, Gait, Ontario, Canada (Toronto, Ontario, Canada) Filed Jan. 25, 1963, Ser. No. 254,020 4 Claims. ((31. 336-180) This invention relates to electrical, inductive, devices and particularly to an inductive device having a plurality of turns of conductor distributed uniformly along the axial length of the winding.

The devices of particular concern herein are shunt reactors in power transmission systems. The novel construction of the device to be described herein however, may be utilized in other inductive devices.

Reactors may be of the core or coreless type, the latter being preferred in many cases for the following reasons:

(a) Iron will produce some distortion in the voltagecurrent characteristic of the reactor. Further, saturation of the iron may occur at high voltage levels, resulting in the reduction of reactance at full voltage. This effect is particularly serious since full-voltage reactance tests are probably impractical'at the required ratings, and dependence on extrapolated values is therefore not justified. However, since coreless windings do have linear characteristics, the results of the reactance test may be safely extrapolated.

(b) Harmonics will be present if iron is used. The third harmonic in particular may be of serious magnitude with solidly grounded Y-connected banks. By contrast, an air-core coil incorporating eddy-current tank shielding is free of harmonics due to the linear volt-amp characteristic.

(c) Laminated iron cores, iron yokes or iron tankwall shields will introduce complications in electrical insulation technique. High stress points are likely to be incurred at edges and salient points of such structures. In any event, iron cores will increase electrical stresses in the coils due to the proximity of ground potential. In this connection, the insulation of the air-core coil is simplified and electric stresses are greatly reduced in intensity through much larger clearance to ground.

(d) The capacitance to ground introduced by the proximity of iron-core surfaces has an adverse effect on the voltage distribution of the coil under impulse test conditions. In particular, the presence of the iron core introduces graded capacitance to ground at the line end of the coil, which results in resonant impulse voltage concentration across the end of the winding, thereby causing dangerously high voltage gradients in this neighbourhood. This condition is greatly improved with a coreless winding, especially if the coil turns are uniformly distributed axially along the winding stack.

(e) Other merits of a coreless reactor are: a negligible noise level and vibration, better internal cooling, greatly simplified construction and maintenance.

Heretofore, it has not been possible to distribute the turns uniformly in the ideal axial direction with any known form of winding configuration other than a single layer helix. Further in most cases a single layer helix of reasonable length is not possible for the current capacity and number of turns required. It is a known fact that, for an efficient coil, the axial length dimension must be several times that of the radial wall thickness, hence voltage uniformly distributed lengthwise will incur far lower stresses than voltage distributed radially: this permits a high capacity coil of moderate size with complete safety.

A disc winding which has partial axial turn distribution is also known, but the difliculty with such is that the total number of turns required is so large that each disc must have prohibitive numbers of radially disposed turns; thereby introducing such high voltage stresses between adjacent discs as to prevent the low stress criterion sought.

High-voltage coils, as developed for transformers, have inherent stress problems. Layer wound coils endeavour to distribute the electric stress radially, but the turns are non-uniform in the radial direction and concentrations of stress must inevitably occur at the ends of each layer; in fact the entire impulse voltage appears across a very limited number of such gaps between adjacent layers. Despite great thickness of layer insulation, undesirably high stress levels and low margins of safety are inevitable between adjacent layers.

It is the main object of the present invention to provide an inductive device where the voltage may be distributed uniformly in the ideal axial direction through a plurality of parallel connected concentric coil elements. While each coil element has the advantage of a single layer helix with regard to low voltage gradient, collectively the coil elements are capable of carrying large currents.

It is a further object to provide an inductive device where each of the independent winding elements have substantially the same axial length, and carry substantially any desired fraction of the rated total current. Such a winding has the lowest obtainable voltage gradient at any point from terminal to terminal. Further, since each parallel winding element is of essentially the same length, there is negligible potential difference between turns in the radial direction.

A further object is to provide an inductive device where the nominal voltage stresses along the length of the winding are exceptionally low even at impulse levels, being far below corona starting point.

Accordingly, the present invention consists of,

A plurality of concentric coil elements electrically connected in parallel to a pair of terminals, each of said elements consisting of a plurality of independent, serially connected, sections, said sections comprising a ring formed from a plurality of turns of insulated, electrically conductive wire.

The invention is illustrated by way of example in the accompanying drawings, wherein:

FIG. 1 is a partial sectional view of a casing enclosing a shunt reactor constructed in accordance with the present invention;

FIG. 1a is a partial sectional view taken substantially along the line 1a-1a of FIG. 1;

FIG. 2 is a vertical partial sectional view of another embodiment of a shunt reactor constructed in accordance with the instant invention; and

FIG. 3 is a cross-section view along section 33 of FIG. 2.

Referring now in detail, shown in the drawings is a shunt reactor 10 encased in a sheet metal housing or tank 11 and is supported, in spaced relationship with respect to the housing, by an insulating pedestal 13.

The housing or tank 11 consists of a cylindrical member 14 having opposed end flanges 15 and 16 to which respective end covers 17 and 18 are secured.

The end cover 18 may be detachably secured as by bolts, rivets or the like through a plurality of circumferentially spaced apertures 19. The cover 18 further includes a detachable conical central portion 20 (or turret) detachably secured thereto as by a plurality of bolts, rivets or the like through circumferentially spaced apertures 21. The turret or cone 20 is apertured to receive and support a bushing 22, an inside extension 23 of which terminates immediately adjacent the central axis of the reactor 10. Se-

' netic shielding.

cured to the internal wall of the casing is a plurality of magnetic shields 24.

The tank, in most cases, will require substantial magnetic clearance from the coil and preferably a round tank is used with aluminum eddy-current shielding against the inside surface. The concentric tank shield of this form facilitates the computation of eddy-current magnitudes and stray loss values. Further, the round tank is the most simple to manufacture, permits optimum cooling radiation, and is easily braced for vacuum and pressure. The smooth tank wall shield, being concentric with the coil and with end grading rings facilitates obtaining low electrical stresses. The lower or bottom wall of the tank is preferably aluminum or aluminium coated steel. The aluminium provides mag- In the latter construction, the aluminium may be a separate inner casing while the outer casing is steel or the like.

The react-or consists of a plurality of concentric radially spaced coils 31, 32, 33 and 34, each of the coil-s consisting of a plurality of vertically stacked elements, at, b, c, d, etc., for example, coil 31 consists of elements 31a, 31b, 31c, 31d, etc. Each element consists of a plurality of turns of insulated copper wire 35 Wound to define an annular member. Each of the elements at, b, c, d, etc. has the opposed ends of the wires direct-ed outwardly forming pigtails whereby vertically adjacent elements may be readily serially connected as at 36 to form the coil.

The elements a, b, c, d, etc. of each of the coils may be axially spaced if desired and the coils 31, 32, 33 and 34 are radially spaced. A plurality of T-shape, in cross section, spacer members 37 (FIG. 3) spaced circumferentially internally of each of the coils 32 and 33 radially spaces the coils. A plurality of spacers 38 are keyed to each axial spacer 37. These spacers 38 are slidable along spacer-s 37 and are adapted to separate vertically adjacent stacked elements a, b, c, d, etc. The axial spacing of the elements and the radial spacing of the coils provide a plurality of paths for the circulation of air, gas, fluid or the like cooling medium.

The coils surround a cylindrical insulating member 50 such as a phenolic impregnated fiber cylinder, the first coil being held in spaced relation With respect thereto by a plurality of previously described spacers. End members 51 and 52 are interconnected by a plurality of the rods 53 and abut opposed ends of the cylinder 50. Opposite ends of the rods are threaded to receive nuts which bear against respective upper and lower rings 54 and 55. These rings are made of an insulating material such as plywood, plastics such as phenolic resins, or the like.

In the embodiment shown in FIG. 2, the members 51 and 52 consist of a pair of spaced fiber board disks 56 and 57, 58 and 59, the disks in each pair being held in spaced relationship .by respective central spiders 60, and 61, through which are provided bolts 62 and 63, providing a line and a ground terminal. The leads 64 and 65 of the coils are electrically connected respectively to spiders 60 and 61. The spiders and terminal bolts preferably are copper or other highly electrically conductive material. The respective pair of disks are joined at the periphery by annular insulating rings 68 and 69. The fiber disks are metallized to provide shielding.

In the embodiment shown in FIGURES l and 1a, the pairs of fiber disks are eliminated and the leads 64 and 65 of the coils are electrically connected to the spiders 60 and 61 and bolts 62 and 63 through a plurality of arms A secured to said spiders and radiating therefrom. Pieshaped segments of metallized plates 13 are included between adjacent pairs of arms A to provide shielding. The metallized plates B can be fixedly attached to the arms A by an adhesive. In the embodiment shown in FIGURE 1, the annular insulating rings 68 and 69 bear against the outer ends of the spider arms A.

The annular ring 68 includes an upper lip whereby the ring may rest upon the upper edge of the end disk 56 as seen in FIGURE 2. Secured by struts 73 to the upper and lower rings 68 and 69 are upper and lower metallic potential grading rings 71 and 72.

By means of the end spiders sandwiched between metallized shields and the use of circumscribing electric grading rings of substantial diameter, the ends of the coil elements are shielded from high voltage gradients.

In the above described structure, each coil element is wound individually and subsequently electrically connected upon assemblage of each of the coils. This facilitates winding and handling. Upon assembly of all of the concentric coils, the leads are connected to the end spindlers, thereby electrically connecting in parallel the concentric coils. Terminal 62 is connected to the line by a flexible conductor 75 or other suitable means.

The calculations for the individual coil elements and the over-all coil design (which consists of a plurality of concentric coils) are based upon solving simultaneous equations.

When designing the reactor of the present invention, the windings in each coil must be arranged to satisfy the simultaneous equations:

where:

P=the number of coils in the reactor;

S=L 2 3 r and .s may or may not be equal,

n and n =the number of turns in coils r and s, re-

spectively;

M =the reactance between coils r and s (when r=s r:s self-inductance of the coil);

i current designed to fiow through coil r; and

E=the designed voltage drop across the reactor. Since each coil is connected in parallel, E is, of course, the same throughout the design equations. In the reactor design, initially, an educated guess as to the number of conductors and the size thereof is made. The conductor is preferably designed to be of standard size and low current rating to minimize losses. This is desirable because it does not necessitate manufacture of special conductors for fabrication of the reactor windings. Conductor size, of course, determines maximum current in a particular coil which governs maximum temperature increase of the reactor from no load to full load.

Of course, the diameter of each coil must be greater than the interior coil to which it is adjacent by an amount greater than the adjacent conductor diameter plus insulation. It is preferable, moreover, to design coil diameter slightly greater than this minimum quantity to permit coolant circulation. Winding pitch cannot be smaller than the width plus insulation of the conductor which comprises the particular coil. Pit-ch can exceed this minimum value thus obviating the necessity for insulated conductors when the coils are spaced apart radially to a sufiicient extent.

After determining the size of each conductor, which ascertains its current, each coil diameter and each winding pitch, the number of windings in each coil is computed from the equation by solving for mutual and self reactance. This may be accomplished by manualor automatic computation methods.

The following is .an example of a typical design of a shut reactor for construction in accordance with the present invention.

SHUNT REACTOR DESIGN Rating: Single phase-60 cyc.-22 m. van-133,000 volts drop-163 amps. Winding: 9 concentric layers of coil elements arranged I claim:

1. An air core shunt reactor comprising a plurality of concentric, radially spaced coils of equal length electrically connected in parallel and confined between a pair according to Table 1 below; 5 of axially spaced, interconnected, opposed end members,

Table 1 Coil Round wire Turns Number Radial coil Axial coil Coil mean pp r element build, in. length, 1n. diameter, 1n.

A.W.G. 2,139 00 .7674 68 77 9 A.W.G 1, 921 54 .8424 65. 7 5 8 9 A.W.G. 1, 716 48 .8424 58.68 06 8 A.W.G 1, 620 45 .9342 61.95 57. 84

8 A.W.G 1,584 44 .9342 60. 57 60. 71

7 A.W.G.. 1, 569 53 1. 0302 75.78 63- 67 7 A.W.G 1, 491 50 1. 0302 72. 01 66. 75

7 A.W.G 1, 455 49 1. 0302 70.28 09. 70

BetWeen each coil there are A2" axial cooling ducts such coils each comprising a plurality of individual annumaint-ained by a number of radial spacers disposed parallel to the axis of the coils. Between each element of each coil there are radial ducts, approximately A Wide maintained by radial key-spacers threaded or otherwise secured to the radial spacers.

The winding coil lengths specified in Table lcolurnn 6 must be met, and may be obtained by suitably adjusting the widths of the radial ducts between elements of each coil.

The constructions of each element of each coil are given in Table 2 below:

Table 2 Turns per element Crosssection dimensions of elements Coil Radial (rows) Axial Total Radial, In. Axial, in. (turns) Note.-Sorne elements of the var1ous coils Wlll drop one turn in order to obtain the total turns given in Table 1-column 3, e.g. Coil 3 requires 1716 turns. But there are 48 elements of 36 turns per element giving 36 48=1728 turns. Hence, drop one turn in 12 of the 48 elements and distribute these turn elements uniformly through the coil length.

The dimensions of the elements given in Table 2 can easily be met with .012" of paper insulation on the wire. Allowance has been made for additional insulation around each element and the element dimensions of Table 2columns 5 and 6 should be built-up accordingly.

The characteristics of this reactor are as follows: Total copper weight=12343 lbs. 1 R losses at 75 C., at rated current and frequency =57 k. W.Overall dimensions=73.88 OD. x

82.78" lg. (over spiders only).

lar elements disposed in axial spaced relationship and electrically connected in series, terminal means disposed on the axis of said coils at each end of the latter for electrically connecting the parallel coils of said reactor in series in an electrical circuit, said terminal means being secured one to each of said end members, a casing enclosing said reactor, an insulating pedestal disposed between the lower end of said coil and the casing thereby to support said coils in spaced relationship with respect to said casing, and a pair of metallic annular members circumscribing the outermost coil in radially spaced relationship with respect thereto, said annular members being disposed respectively adjacent opposed ends of the coils.

2. A shunt reactor as defined in claim 1 including a plurality of metallic shielding rings secured to the inner surface of the casing and being disposed in spaced relationship along the axis of said coils.

3. A shunt reactor as defined in claim 1 wherein each of said end members consists of a pair of substantially parallel metallized plates having -a space therebetween.

4. A shunt reactor as defined in claim 1 wherein each of said end members includes a spider having the legs thereof radiating outwardly from the axis of the coils and wherein the terminal means associated therewith is a hub from which the arms of the spider radiate said arms electrically connecting said coils in parallel.

References Cited by the Examiner UNITED STATES PATENTS 1,242,497 10/1917 Torchio et al. 3361'85 X 2,352,166 6/ 1944 Camilli 336-84 2,422,037 6/1947 Palvev 336--186 X 2,783,441 2/1957 Camilli et al 336- 2,937,349 5/1960 Camilli 336-84 X 2,986,716 5/ 1961 Carlon 336- 3,013,102 12/1961 Doll 33684 X ROBERT K. SCHAEFER, Acting Primary Examiner.

JOHN F. BURNS, LARAMIE E. ASKIN, Examiners. 

1. AN AIR CORE SHUNT REACTOR COMPRISING A PLURALITY OF CONCENTRIC, RADIALLY SPACED COILS OF EQUAL LENGTH ELECTRICALLY CONNECTED IN PARALLEL AND CONFINED BETWEEN A PAIR OF AXIALLY SPACED, INTERCONNECTED, OPPOSED END MEMBERS, SUCH COILS EACH COMPRISING A PLURALITY OF INDIVIDUAL ANNULAR ELEMENTS DISPOSED IN AXIAL SPACED RELATIONSHIP AND ELECTRICALLY CONNECTED IN SERIES, TERMINAL MEANS DISPOSED OF THE AXIS OF SAID COILS AT EACH END OF THE LATTER FOR ELECTRICALLY CONNECTING THE PARALLEL COILS OF SAID REACTOR IN SERIES IN AN ELECTRICAL CIRCUIT, SAID TERMINAL MEANS BEING SECURED ONE TO EACH OF SAID END MEMBERS, A CASING ENCLOSING SAID REACTOR, AN INSULATING PEDESTAL DISPOSED BETWEEN THE LOWER END OF SAID COIL AND THE CASING THEREBY TO SUPPORT SAID COILS IN SPACED RELATIONSHIP WITH RESPECT TO SAID CASING, AND A PAIR OF METALLIC ANNULAR MEMBERS CIRCUMSCRIBING THE OUTERMOST COIL IN RADIALLY SPACED RELATIONSHIP WITH RESPECT THERETO, SAID ANNULAR MEMBERS BEING DISPOSED RESPECTIVELY ADJACENT OPPOSED ENDS OF THE COILS. 